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Deciding Which Species to Save

Felix Marx just finished his Ph.D. in paleontology at the University of Otago in New Zealand.

Updated January 11, 2013, 10:36 AM

As far as we have managed to read it, the fossil record tells us that whales and dolphins were probably more diverse in the past than they are now. These ups and downs of cetacean diversity over time are the result of different families originating, diversifying and, eventually, declining again, sometimes to extinction. For example, the living Ganges and Indus river dolphins are the last survivors of a group that was rather diverse between 15 and 30 million years ago. Shortly thereafter, the family went into decline —at the same time as modern oceanic dolphins, the most diverse cetacean family alive today, started to take off.

The Ganges and Indus river dolphins are the last survivors of a once-diverse group. Should they be priorities, or should we bet on the more resilient groups?

Of course, these are extremely long-term trends, but they can tell us something about the levels of threat living cetaceans are facing. Being the last of their kind with no close living relatives, the Ganges and Indus river dolphins are the last guardians of a wealth of genetic, morphological and ecological diversity. The same can be said for many other living cetaceans, such as the pygmy right whale, or sperm whales. Should any of these animals ever be driven to extinction, the loss of evolutionary history would be considerable and, arguably, much more significant than if a species with many living relatives were to disappear. Who knows what evolutionary and ecological potential may lie dormant in this ancient survivor? The recent extinction of the Yangtze River dolphin, itself the last survivor of an ancient lineage, provides a haunting example.

Taking such an evolutionary point of view invites the question of what “threat” actually means. Should we assign a greater level of threat to the endangered Ganges River dolphin because of its evolutionary history than to, say, the vaquita – which has many living relatives? Naturally, there are many other reasons for conservation besides genetic or morphological uniqueness, and many of these, such as the ecological or “emotional” significance of a particular species, may outweigh any evolutionary argument.

In fact, the argument for preserving these relatively distinct species can easily be turned on its head. A focus on saving relics like the Ganges River dolphin might be misguided, if it shifts attention from other, ostensibly more evolutionary flexible groups. Take rorquals, for example, or killer whales, which at the moment seem to be in the process of diversifying into different species. Arguably, such evolutionarily active lineages represent the future, and may prove a better bet in terms of adapting to large-scale environmental change than the Ganges River dolphin.

Whichever line of argument people may follow, evolutionary history and potential should not be ignored when making conservation decisions.